1. Field of the Invention
The present invention relates to a centrifugal separator, and more particularly to a belt driven centrifugal separator in which driving power of a motor is transmitted to a rotor via a driving power transmission mechanism, such as belt.
2. Description of the Related Art
Rotor driving systems of a centrifugal separator can be classified into a direct driving type in which a rotor is directly coupled to the rotational shaft of the motor, and an indirect driving type in which the rotor and the motor are coupled via a driving power transmitting mechanism including, for example, a belt. The centrifugal separator of the direct driving type is more frequently used in the art than that of the indirect driving type due to simplicity in structure and high driving power transmission efficiency. However, the direct driving type centrifugal separator requires a motor to be disposed in alignment with the rotational shaft of the rotor, so that the position in which the motor is disposed is restricted and the vertical dimension of the centrifugal separator increases.
When a user desires a low height centrifugal separator, such as a tabletop centrifugal separator, for the reasons of easy-to-access to a rotation chamber, the direct driving type centrifugal separator is more suitable than the indirect driving type. The indirect driving type can provide a low height centrifugal separator because a motor can be disposed aside the rotation chamber with the use of a driving power transmission mechanism including a belt or the like to transmit the driving power of the motor to the rotor. The indirect driving type is adopted when a motor designed to use for another purpose is used for the centrifugal separator or when the direct driving type is not available for the reasons of internal arrangement of the components.
For the indirect driving type centrifugal separator, the rotational speed of the motor is controlled so that the rotational speed of the rotor is set to a target value. Typically, the rotational speed of the rotor is detected magnetically or optically. With the magnetic detection, magnets are secured to the rotor or the rotor shaft and a Hall element is disposed to confront the rotating magnets and generate pulses with a frequency proportional to the rotational speed of the rotor. With the optical detection, a photo-interrupter is used in which light emitting and light detecting elements are disposed in opposition with a disk interposed therebetween. The disk is formed with slits and coaxially attached to the rotor shaft. The light detecting element generates pulses with a frequency proportional to the rotational speed of the rotor. The pulses generated from the Hall element or the light detecting elements are applied to a microprocessor for computation of the rotational speed of the rotor. The rotational speed of the motor is controlled to be a desired value based on the rotational speed of the rotor computed by the microcomputer.
Even if the above-described control is carried out, the belt or other components of the driving power transmission mechanism would suffer from damages when slippage of the belt occurs. If the centrifugal separator is used while leaving the damaged belt as it stands, the motor might be damaged due to overload imposed thereupon or the belt might be fatally damaged. As a result, the rotor may not be able to rotate or to reach to a predetermined rotational speed even if the rotational speed of the motor is increased.
In order to prevent the damage of the motor, Japanese Patent Application Publication No. Hei-10-118529 proposes an abnormality detection system in which abnormality of the driving power transmission mechanism is detected by comparing the rotation signals of the motor and the rotor. However, the proposed abnormality detection system produces abnormal signals whenever the comparison results indicate that the rotational relation of the motor and the rotor is offset from the exactly normal status. Normally, a small amount of slippage does not cause any problem, thus can be neglected. The abnormality signals produced from the abnormality detecting system includes not only real abnormality signals but also redundant and unneeded abnormality signals.
Japanese Patent Application Publication No. 2003-10734 proposes a centrifugal separator with an abnormality detecting device in which redundant and unneeded abnormality signals are not generated.